1. The Field of the Invention
The present invention relates to a door lock device for a household appliance, in particular a washing machine.
2. The Relevant Technology
As known, in clothes washers and/or dryers, dishwashers, ovens and other household appliances fitted with a door accessible from the outside there is a safety device that prevents the door from opening when the appliance is in operation.
This may be for safety reasons, since in the case of a clothes washer someone could otherwise open the door and cause damage due to water coming out or injury to the user if a spin cycle is going on, or for reasons related to the timed operation of the household appliance, e.g. in the case of gas or microwave ovens carrying out cooking cycles whose duration is set by the user.
These devices which carry out such functions in the various household appliances are commonly called “door locks”; for simplicity, this definition will therefore be used in the following description and in the appended claims.
As can be easily understood, said devices may have several configurations depending on the type of household appliance they are intended for; however, it can be stated that they essentially comprise a latch connected to a mechanism, which cooperates with the door of the household appliance to lock it.
The mechanism, that is driven by an actuator, may be quite complex and may include many elements, such as sliders, ratchets, countersprings, reducing gears and the like, depending on design choices, whereas the actuator is typically an electromagnet or a thermoactuator.
The latter is controlled by the household appliance's control system, which coordinates its operation with the general operation of the washing machine, dishwasher, oven or the like where it is installed.
In some door lock types, like the one described in European patent application EP 1 467 048, the mechanism comprises a movable element, such as a latching slide, which under the countering action of elastic means, generally a spring, engages with a homologous element of the door (a hook or an aperture, as the case may be): the actuator locks/unlocks the movable element depending on the cycle step being carried out, by engaging it with the homologous one on the door and thus locking/unlocking the latter.
The movable element of the device is held in the door lock condition for the time set by the household appliance's control system, which will then activate/deactivate the actuator in order to have it make a reverse movement thereby allowing the door to be opened.
In the reverse step, the actuator arms the door lock device again by loading the elastic means, which are then ready for the next operating cycle.
From a functional viewpoint, the door lock devices referred to above have been extensively tested and meet the requirements they are intended for; however, their construction is rather complex, in that the mechanism associated with the actuator must allow closing the door (like any door latch) while at the same time preventing unauthorized opening depending on the cycle steps being carried out by the household appliance.
This involves the presence of additional components, such as reducers or mechanical transmissions or the like, the operation of which must be coordinated with that of the movable element in order to enable the door opening and closing movements.
As can be easily understood, the presence of such additional components makes the door lock device more complex and, as a result, rather bulky.
Furthermore, in the case of clothes washers the operation of the door lock device may be impaired by formation of detergent scale on the mechanical components thereof, leading to easily imaginable problems.
For example, a hardened detergent deposit may be formed on the hook or on the slide aperture, which in the engaged condition will change the position of the slide, resulting in the risk that the door will not lock properly because the actuator does not act upon the slide as it should.
Different solutions are also known in the art, like the one disclosed in European Patent No. 965 677.
In this solution, the slide is moved by the hook as the latter is inserted into the window, until it reaches a working position wherein it can be locked, so as to hold the hook in position and prevent the door from opening.
As can be easily understood, the proper operation of this solution is however strictly dependent on the correct positioning of the hook with respect to the slide when the door is closed.
A wrong position will in fact cause the slide to move too little, thus not reaching the position where it can be locked; this will prevent locking of the hook and will compromise the safety of the machine on which such a device is installed.
This problem is even more felt when the door and/or the seat of the door lock device are made of plastic, as is often the case as far as clothes washers are concerned.
In this case, indeed, the hook is frequently manufactured as one piece with the door during a single moulding process.
The shrinking of the plastic material occurring after said moulding process may cause an inaccurate positioning of the hook, leading to the risk that the above-described door lock device will not work properly due to an improper movement of the slide to the lock position.
Moreover, the plastic material is subject to deformation over time, which may cause the hook to be relocated, thereby bringing about the above-mentioned consequences.
In this regard, it should be noted that said problems are even more important when a top-loading washing machine is concerned.
In these machines, in fact, the door is very large and is therefore almost always made of plastic in one piece with the hook, as described above.
The large dimensions of the door, combined with the facts that the door hinges are also made of plastic and that the hook is typically arranged on the side opposite to the hinges' side, often cause the hook to be improperly relocated as it is inserted into the slide window; as a consequence, the operation of the door lock device may easily be jeopardized.
The different shrinking of the plastic material of the door and of the hook following the moulding process and the variability in the door lock device's mounting position make the situation even worse.
Taking into account also possible deformations deriving from operating circumstances (such as heat or careless use), it is apparent that these devices are subject to the influence of many variables which may compromise their operation, if the position of the hook and the position of the slide are not accurate.
It must also be pointed out that an inaccurate positioning implying, for example, an improper interfacing between the hook and the window, cannot generally be rectified by simply using the force applied by the actuator, because in these applications the latter typically consists of an electromagnet exerting a rather small force, not capable of forcing the slide to the correct locking position in the event that, for any reason, it is engaged by the hook in an incorrect position.
What is more, this problem cannot be overcome by simply providing a larger window on the slide, since in such a case the actuator will not be able to lock the slide properly because the slide will still have a certain travel tolerance after locking has occurred and may disengage when the door is pulled.
Any detergent scale will only make things even worse, in particular as far as top-loading washing machines are concerned, where such scale is more likely to form because some detergent may inadvertently fall into the door lock as the dispenser is being filled and/or as it is being inserted into the drum.